1. Field of the Invention
The present invention relates to the field of construction, and more particularly to the on-site construction of multi room homes and the like having relatively low cost and unique esthetic character.
2. Prior Art
The present invention relates to the fabrication of structures generally identified as "dome structures". While the preferred method of practicing the present invention is with respect to the fabrication of complete dome-like structures on a foundation, the method is also useful for such purposes as providing dome or arched roof structures over more conventionally formed walled regions or for the complete fabrication of such structure. Accordingly, only the prior art relating to such structures shall be described herein.
Various methods of fabricating dome structures are known in the prior art. These techniques vary considerably, depending on the character of the resulting structure desired. By way of example, dome structures have been fabricated by providing a mound of dirt in the desired shape, pouring a reinforced concrete shell thereover, and finally removing the dirt under the then self-supporting shell. Other more commonly utilized techniques generally include the assembly of some form of wood or steel supporting structures over which a dome covering of wood, metal, glass or plastic, or combinations thereof is provided. Generally the supporting structure becomes an integral part of the finished building, though some of the structure, such as vertical supports, may be removed when the dome is complete.
A dome structure has also been fabricated through the use of a balloon, wherein a foundation of conventional construction is provided, a balloon is inflated over the foundation, and a structural material such as gunnite or concrete with steel reinforcing is placed thereover to provide the structural shell of the resulting building. Following the curing of the gunnite or concrete, the balloon is deflated and removed through an opening left for this purpose. Such structures have been fabricated in significant numbers by Wallace Neff, a prominent architect, who holds a number of U.S. patents on the various techniques involved. Techniques developed with respect to these systems of the prior art included techniques for providing plumbing and electrical connection, etc. In order to achieve the desired shape, different from that of the balloon, material was placed on the balloon from the top down (see U.S. Pat. No. 2,388,701). However, this general type of structure and fabrication method has not generally been continued in recent years, perhaps because of certain problems and limitations experienced in actually fabricating the structure.
One of the problems sometimes encountered with prior art balloon construction techniques involves the problem of maintenance of balloon inflation and balloon stability over the time required for common cementitious materials to cure. Cement, being made typically from relatively local materials, may exhibit great differences in curing and strength characteristics, sometimes requiring twenty-four hours or more to reach an adequate structural strength. Therefore balloon inflation has to be maintained not only while the cement or gunnite is placed over the balloon, but has to be maintained for some period thereafter which may be as long as 1 day or more. Any substantial variation in balloon pressure or loss of inflation during this curing time would obviously have disasterous results, resulting in the loss of the structure and a substantial cleanup problem before a new structure could be started. Also the balloons themselves are far from rigid when inflated, as pressures are necessarily low because of the sizes of the balloons used. Thus the balloons, as a construction form, are less than ideal for shooting gunnite against or for building cement up against because of their movement and deflection under the loads, particularly the impact loads involved. Also, the shape of the resulting structure depends somewhat on balloon pressure and material thickness and density, and because of variations on these parameters conformance to the "structural model" is less than ideal.
Another problem encountered with such structures involves environmental changes and the heating and cooling of the resulting structure. If the construction technique utilizes a single cement or gunnite reinforced shell, the thermal conductivity of the resulting shell is relatively high, resulting in heat (or cooling) loss through the shell. Also the cooling of the shell from the outdoor environment can cause condensation on the inner shell surfaces, resulting in sweating and perhaps staining of the inner walls. To overcome this problem, shell structures were fabricated utilizing balloons by providing a first inner concrete or gunnite shell, covering the shell with sheets of insulation, and then providing a second outer shell over the insulation. This technique avoids the sweating problem and provides a high degree of insulation in the resulting structure. However, it has the disadvantage that the inner and outer shells are substantially structurally independent shells, and therefore each must be structurally sound and self-supporting.
Also, the dome structures of the prior art are generally single dome structures. To the extent that structures comprising multiple domes may have been favricated, such structures were generally fabricated by the construction of adjacent domes, subsequently coupled by tunnels or the like. In general, the prior art did not include construction techniques which facilitated the easy fabrication of interconnected dome structures to form integrated multiple dome dwellings.
Another problem of the dome structures of the prior art is the problem of engineering. In construction, and particularly dome construction, it is critical that the load and stress factors be calculated very accurately. The prior art domes always changed shapes considerably with the weight of the cement placed on them. Therefore the curve of the dome was quite different from the original dome form, making it impossible to pre-calculate or accurately engineer the proposed dome before it was built. Also, the change in balloon shape created severe problems with the alignment of windows and door frames and molds which were fastened to the balloon.